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Hi there, DA is a relative metric, it changes over time. If your competition is doing more/better work than you, then DA would go down. Here is an excerpt from here (https://moz.com/learn/seo/domain-authority Since Authority is based on machine learning calculations, your site's score will often fluctuate as more, less, or different data points are used in the calculation — for instance, if Facebook were to acquire a billion new links, everyone's PA and DA would drop relative to Facebook. For this reason, keep in mind that you should always use Domain Authority as a relative metric to compare against the link profiles of other sites, as opposed to an absolute value scoring the efficacy of your internal SEO efforts. Hope this helps.